A plastic lens is lightweight, highly tough and easy to be dyed. Properties required of a plastic lens are low specific gravity, high transparency, and low yellow index. Optical properties required of a plastic lens are high refractive index, high Abbe number, high heat resistance, and high strength. A high refractive index allows the lens to be thinner, and a high Abbe number decreases the chromatic aberration of the lens.
Recently, many organic compounds containing sulfur atoms produced for the purpose of providing a high refractive index and a high Abbe number have been reported. Among these compounds, polyepisulfide compounds containing sulfur atoms are known to provide a good balance of the refractive index and the Abbe number (Patent Document 1). Since polyepisulfide compounds are reactive with various types of compounds, compositions of polyepisulfide compounds and various types of compounds have been proposed for the purpose of enhancing the properties (Patent Documents 2 through 5).
However, episulfide compounds, which are highly reactive, are difficult to be stored for a long time. A technique of storing episulfide compounds in a refrigerated state (Patent Document 6) and a technique of adding an epoxy compound containing a halogen group (Patent Document 7) have been proposed.